Okay, I spoke to Nate French a bit about the format and also card distribution.
The base game comes with 4 "preconstructed decks" and three quests. The quests have a Shadow pack that goes with them and so when you pick your quest cards, you use the pack for each of the 3 cards to build the shadow deck.
The preconstructed decks have singles, so 3 base sets will be required for a full playset, but the packs will be all 3 ofs, like the rest of the LCGs now.
Also, the shadow cards have symbols that are associated with the quests like a Spider or Orc and you will be able to mix in later Spider cards to the shadow deck when facing a spider quest.
For competitive play, Nate said they were leaning towards what I assumed. There would be a new quest you have never seen before at the event. Build what you hope is the best deck, show up and get a quest assigned and go at it. The quests would also be prizes to be reprinted later, but special for that event. I like that a lot. It is a elegant way to add story to the game.
That's it for now. I haven't re-demoed so it's all I've got.
Chevee